Abstract
Introduction Small case series have reported that diabetic ketoacidosis is
associated with an elevated osmolar gap, while no previous studies have assessed
the accuracy of calculated osmolarity in the hyperosmolar hyperglycemic state.
The aim of this study was to characterize the magnitude of the osmolar gap in
these conditions and assess whether this changes over time.
Methods In this retrospective cohort study, two publicly available
intensive care datasets were used: Medical Information Mart of Intensive Care IV
and the eICU Collaborative Research Database. We identified adult admissions
with diabetic ketoacidosis and the hyperosmolar hyperglycemic state who had
measured osmolality results available contemporaneously with sodium, urea and
glucose values. Calculated osmolarity was derived using the formula 2Na
+ glucose + urea (all values in mmol/L).
Results We identified 995 paired values for measured and calculated
osmolarity from 547 admissions (321 diabetic ketoacidosis, 103 hyperosmolar
hyperglycemic states and 123 mixed presentations). A wide variation in the
osmolar gap was seen, including substantial elevations and low and negative
values. There was a greater frequency of raised osmolar gaps at the start of the
admission, which tends to normalize by around 12–24 h. Similar
results were seen regardless of the admission diagnosis.
Conclusions The osmolar gap varies widely in diabetic ketoacidosis and the
hyperosmolar hyperglycemic state and may be highly elevated, especially at
admission. Clinicians should be aware that measured and calculated osmolarity
values are not interchangeable in this population. These findings should be
confirmed in a prospective study.
Key words
diabetic ketoacidosis - hyperglycemic hyperosmolar nonketotic coma - osmolarity -
osmolar gap
